Reference to Previous Application
The present invention is an improvement over an invention disclosed in a patent application entitled Real Time Automated Inspection, Ser. No. 374,373 filed May 3, 1982, now U.S. Pat. No. 4,519,041 issued May 21, 1985 and assigned to the same assignee as the present invention. The disclosure of that application is deemed to be incorporated herein by reference to the extent necessary.
The invention relates generally to a real time digital image enhancement system and, more particularly, to an improved method for performing the image enhancement segmentation processing required for a real time automated system for detecting and classifying surface imperfections in objects such as hot steel slabs.
The American steel industry is one of the largest consumers of energy in the United States. The trend in steelmaking technology in the United States is toward the continuous casting of steel. In a continuous caster, molten steel is continuously poured into a mold which is water cooled. The steel as it solidifies is drawn out of the mold in a perpetual ribbon on a roll table and is cut to form slabs. The steel slabs often have surface imperfections or defects which must be detected and evaluated prior to further processing of the slabs. In most steel mills the hot slab coming out of a caster is cooled to facilitate human inspection for surface defects and imperfections. If the surface imperfections are found to be sufficiently serious to make it necessary to condition a slab before continuing with the processing, as by machining, for example, the slab is routed to a processing area where such conditioning is performed.
If, on the other hand, the surface imperfections are minor or not serious such that intermediate conditioning is not required, the slab is reheated for further processing. Thus, if it were known beforehand that intermediate conditioning was not required, the substantial cost of reheating the slab for further processing could be saved.
An automated inspection system capable of inspecting a slab coming out of the caster while it is still hot avoids the intermediate cooling and reheating process currently necessary for manual inspection and thus eliminates the waste of energy associated therewith in those cases where the surface imperfections intermediate conditioning is not necessary.
The concept of an automatic inspection system involves a data collection camera which views the steel slab moving in a transverse direction relative to the scan line of the camera. The data camera, which has picture sensing elements, collects data and the data in the form of digital values is then routed via interface electronics to the digital image enhancement processing stage.
Image enhancement entails several operations that improve the appearance of an image to a human viewer, or operations to convert an image to a format better suited to machine processing, but still recognizable as an image.
Segmentation processing as it applies to image processing is the process of enhancing or segmenting out objects or features of interest from an image. The two primary forms of segmentation processing are edge detection and intensity region thresholding based processes.
Image edges are places within an image where there are relatively abrupt changes in the intensity level. There are existing algorithmic operators such as the Roberts edge operator which are used for edge detection within image frames. The operator requires computations on every picture element or pixel within the image to determine the edge value of each pixel. The edge value computed is compafed to a threshold value to determine if it may be considered an edge within the image.
Likewise, it is possible to compare each picture element or pixel gray scale value to a gray scale threshold and extract areas of uniform gray scale from an image. This later form of image segmentation is called gray scale or intensity region thresholding, and also requires computation on each picture element or pixel within an image.
Existing real time digital image processing systems employ only one type of segmentation process, edge or intensity thresholding due to the severe time constraints of real time digital image processing.